Grettings peeps
i am a 3D Modeler and Programmer that Love Machine and i see that you are trying to make a open version of it i find the idea awesome and i want to participate :)
Here are some model that i make https://sketchfab.com/ddc_cl
also i Manage the C# Programming Lenguage and unity

Models should typically be in fbx format for most compatibility with Unreal Engine 4, and any game code is written in C++.

In the future, Unreal Engine's "Blueprints" will likely be used for variations of objects, such as structures/buildings and units (Similar to prefabs in Unity). The advantage of using blueprints is that these can be accessed by developers, and by users with a machines version of the UE4 editor.